Murray has long been considered the fourth of the Big Four (behind Roger Federer, Rafael Nadal and Novak Djokovic). Murray has reached 11 Grand Slam finals but only won three. He is 28-55 against Federer, Nadal and Djokovic, having a losing record against each.

But at this moment, Murray is the best player in the world for the first time in his career. No, he is not the world No. 1 in the rankings -- Novak Djokovic still holds that title. But Murray, who has made all three Grand Slam finals this year, is the man to beat in Flushing, not Djokovic. Murray is coming off a Wimbledon crown and Olympic gold medal. Since Roland Garros, Murray is 24-1, beating No. 6 Milos Raonic three times and No. 7 Kei Nishikori, No. 8 Tomas Berdych, No. 9 Marin Cilic, No. 11 Jo-Wilfried Tsonga and former world No. 4 Juan Martín del Potro once each. His only loss came to Cilic in his final match before the U.S. Open in Cincinnati.

Meanwhile, Djokovic, who defeated Murray in the French Open final, lost to No. 30 Sam Querrey in the third round at Wimbledon and fell to del Potro in the first round at the Olympics. Djokovic needed four sets to get past No. 247 Jerzy Janowicz in the first round, calling upon the trainer to nurse his right arm. That is on top of a wrist injury that has been nagging Djokovic all summer.

Djokovic caught a break Wednesday, as his second round opponent, Jiri Vesely, withdrew due to left forearm inflammation. Murray won his first two matches, against No. 81 Lukas Rosol and No. 45 Marcel Granollers, each in straight sets.

It was true before the start of the U.S. Open, but now it is confirmed: Andy Murray is the best player on the face of the earth at this moment.

Serena and Venus went to Rio with high hopes. In doubles, they were the No. 1 seed and in pursuit of their fourth gold medal, but lost their first-round match in straight sets to Lucie Safarova and Barbora Strýcová. In singles, both were peaking. Serena had overcome losses in the finals at the Australian and French with a win at Wimbledon, where Venus made her first Grand Slam semifinal since 2010. But an ailing Venus lost her opening-round singles match in about three hours to Kirsten Flipkens. Serena lost in the third round to 21-year-old Ukrainian Elina Svitolina. Venus rebounded to win mixed doubles silver, but for the most part, the Olympic trip was underwhelming for the family.

In Flushing, Venus needed three sets to get past No. 93 Kateryna Kozlova in the first round, but she edged Julia Goerges handily in two sets in the second round. Serena said she didn't play her best but posted consecutive 6-3, 6-3 wins against No. 29 Ekaterina Makarova and No. 87 Vania King 6-3, 6-3.

If both continue to advance, they would meet in the semifinals. In 2015, the two met in the quarterfinals, and Serena won in three sets.

Rafael Nadal is done, right? He hasn't reached a Grand Slam final since 2014, hasn't won a non-clay court tournament since June 2015 and hasn't won a hard-court tournament since January 2014.

Wrong.

Nadal withdrew from the French Open third round with a wrist injury and sat out Wimbledon. The time off appears to be worth it, as Nadal reached the bronze-medal match on hard court in Rio. Nadal won his first six sets in Queens, beating No. 107 Denis Istomin and No. 87 Andreas Seppi. He also closed the Arthur Ashe Stadium roof, along the way.

With Raonic, who was in his quarter of the draw, losing in the second round, the door is open for Nadal to make his first Grand Slam semifinal off clay since the 2014 Australian Open.

Djokovic and Murray may fight over the No. 1 spot, but Nadal could steal a title next week.

Madison Keys is the next big American women's tennis star. That is not an opinion. She has done enough during the past three years to prove it. She is ranked ninth, made an Australian Open semifinal and a Wimbledon quarterfinal in 2015 and has reached the fourth round in four consecutive Grand Slam event. In Rio, she lost in the bronze-medal match.

Keys nearly bowed out in the first round in Flushing, coming back from a set and a break down, and 5-4 in a second set tiebreaker down, to knock off No. 60 Alison Riske. Keys looked more comfortable in the second round, handling wild-card entry Kayla Day 6-1, 6-1.

With Garbiñe Muguruza's second-round loss, Keys, like Nadal, has a favorable quarter. Looking way ahead to the semis, potential match-ups with Angelique Kerber and Roberta Vinci await -- and not the Williams sisters, which means Keys won't have to worry about losing American fan support.

5)American Men Are A Semi-Success Story

USA's Ryan Harrison upsets World No. 5 Milos Raonic to move into 3rd Rd of major tournament for 1st time in career. pic.twitter.com/Rb5GIqH78n

The names you know are struggling. John Isner needed nine sets to get through the first two rounds. Jack Sock escaped a five-set thriller with 18-year-old American Taylor Fritz before a second-round win. Sam Querrey, fresh off his upset of Djokovic at Wimbledon, lost in the first round to No. 250 Janko Tipsarevic.

But wild card No. 120 Ryan Harrison, who had never made it out of the second round in five tries, upset Wimbledon finalist Raonic for his first third round bid. Qualifier No. 122 Jared Donaldson upset World No. 14 David Goffin in the first round in four sets and followed with a straight-sets victory over No. 32 Viktor Troicki. No. 56 Donald Young, a name we knew and then forgot, got out of his first-round match with No. 78 Jann-Lennard Struff unscathed, but fell to No. 23 Ivo Karlovic in the second.

Steve Johnson, a late-bloomer who reached the quarterfinals at the Olympics, is ranked No. 22 and seeded No. 19, but faced a tough draw. He held off No. 79 Evgeny Donskoy in the first round, but fell to former champion Juan Martin del Potro in the second, despite a strong effort under the lights.

Other than Fritz, perhaps none of these players had, have or will have any Grand Slam title potential, but they have given the hometown fans some legit men's tennis this week.

6)CiCi Bellis Made Her College Decision Even Harder

A month ago, American teen sensation CiCi Bellis verbally committed to Stanford, planning to enroll in 2017. But unlike most college recruits, Bellis has already won three U.S. Open matches.

In 2014, the 17-year-old upset then No. 13 Dominika Cibulková in three sets. After failing to qualify for last year's main draw, Bellis won her first two matches this year against No. 65 Viktorija Golubic and No. 49 Shelby Rogers. The current world No. 158 gets No. 2 Angelique Kerber in the third round.

Bellis can sign a letter of intent for Stanford in November, but if she keeps up her current pace, it is hard to imagine she stalls her WTA career for the Pac-12. To this point, she has maintained her amateur status, not accepting earnings and not losing her NCAA eligibility.

7)The Roof Is A Work In Progress

The Arthur Ashe Stadium roof was long overdue and it looks beautiful, but kinks need to be ironed out.

Early matches under the roof have proved to be loud for the players, but more so, the fan experience has been challenged. In the upper deck, the pitter-patter of rain and blasting of the air conditioning system overtook the sound of racquets. For everyone, this is something that will take some time to get used to.

"It apparently was raining unbelievably hard outside," Murray said after his match Thursday. "It seemed that way anyway."

It was raining, but not unbelievably hard. The loudness has been a problem, but Murray also did note the roof cuts the humidity, unlike Wimbledon, where the roof actually makes conditions warmer.

Nadal noted the roof is higher than at the Australian Open or Wimbledon (Arthur Ashe Stadium is much bigger). This means the roof has a minimal effect on visibility.

Serena Williams thinks everyone is overreacting.

"I think it was louder with it open actually in my first night match," Williams says. "It's still extremely loud. But I don't know if it's the roof, per se, or if it's something else."

The USTA is sure to adjust as the tournament goes on, but the most important goal will be accomplished. The tournament will finish on a Sunday, no matter what.